In die-sinking type electrical-discharge machines which use both water and oil based working fluids, a common machining sequence is for roughing to be carried out using the water based working fluid, and finishing to be carried out using the oil based working fluid. This sequence is used because the water based working fluid results in a relatively rough machined surface but with improved machining speed, while the oil based working fluid results in relatively fine machined surface but with a decrease in working speed.
FIG. 11 is a schematic representation of an apparatus for carrying out electrical-discharge machining based on the condition of a workpiece W1, and proceeds according to the sequence of FIG. 11 (A), (B), (C), (D).
In the following description, the water and oil based working fluids are simply referred to as "water" and "oil" respectively. Also in the drawings, water and oil based working fluids are noted simply as "water" and "oil", respectively.
In the above background art, the workpiece W1 is disposed in a work tank T in which an electrode EL1 is designed to move generally vertically. Water 10 is supplied from a service tank 30a for accumulating water, to a machined recess A formed in the workpiece W1, through a check valve 35 and electrode EL1 by means of a pump 31. The water 10 is further supplied from the tank 30a through a check valve 37 by means of a pump 33, and fills the work tank T. In addition, oil 11 is supplied from a service tank 30b, for accumulating oil, to the machined recess A through a check valve 36 and electrode EL1 by means of a pump 32. The oil 11 is further supplied from the tank 30b through a check valve by means of a pump 34, to fill the work tank T.
The water 10 which has accumulated in the work tank T is returned to the tank 30a through a drain 14 and a tank 20a for recovered water. In addition, the oil which has accumulated in the work tank T is fed into the tank 30b through the drain 14 and a tank 20b for recovered oil. The apparatus is constructed so that the working fluids in the tanks 30a and 30b are fed into a separating device 23 through a filter 21, to filter out water, and a filter 22, to filter out oil, respectively. The separated water and oil is then returned to the tanks 30a and 30b, respectively.
In this background art, the workpiece W1 is disposed in the work tank T, and as shown in FIG. 11(A), when the pumps 31 and 33 are actuated to supply the water 10 into the work tank T from the tank 30a, the pumps 32 and 34 remain stopped.
Then, roughing is carried out by applying machining voltage pulses between the workpiece 1, immersed in water, and the electrode EL1 according to appropriate working conditions. When the roughing cut has been finished, as shown in FIG. 11(B), the pumps 31 and 33 are stopped and the water 10 is discharged into the tank 20a from the work tank T through the drain 14. The condition wherein the electrode EL1 has machined into the machined recess A in the workpiece W1 is retained at this time.
Thereafter, as shown in FIG. 11(C), a pump 38 is actuated to supply the oil 11 into the work tank T while the electrode EL1 is still in position to machine into the machined recess A. Likewise a pump 36 is actuated to supply the oil 11 to the machined part A through the electrode EL1.
The water 10 may remain in the machined recess A in the workpiece W1, even after the water 11 is drained and, therefore, a system such that by continuously supplying the oil 11 into the machined recess A by means of the pump 36, any water 10 remaining in the recess will be forced out of the machined recess A by the resulting injection pressure employed to supply the oil. The exchange of the water 10 and the oil 11 is thus completed.
After removing the water 10 from the machined recess A, the electrode ELI is caused to go up once as shown in FIG. 11(D), then the pumps 36 and 38 are actuated to supply the oil 11 into the work tank T from the tank 30b and then finishing is carried out on the workpiece W1 immersed in oil.
FIG. 12 is a working schematic representation of other background art.
In this background art, an example of a workpiece W2 which has already been machined with respect to part of its recess to be machined, then, electrical-discharge machining is carried out with the electrode EL1 as shown, and acts in the sequence of FIG. 12 (A), (B), (C), (D).
In this background art, a solenoid valve 40 and a pump 41 are provided, and are arranged such that the water 10 is suctioned through the electrode EL1 into the tank 20a.
First, as shown in FIG. 12(A), when roughing is carried out on the workpiece W2, a solenoid valve 39 is opened, and pumps 31 and 33 are actuated to supply the water 10 into the work tank T from the tank 30a. At this time, the pumps 32 and 34 are stopped, the solenoid valve 40 is closed and the pump 41 is stopped.
Then, after the roughing cut with the electrode EL1 has been finished, the drain 14 is opened, and the solenoid valve 39 is closed and the pumps 31 and 33 stopped with the electrode EL still in position to machine into a machined recess A1 which was newly produced by the roughing cut as shown in FIG. 12(B). The solenoid valve 40 is opened and the pump 41 actuated. Thus, the water 10 remaining in the machined recess A1 is suctioned from the end of the electrode EL1, and the suctioned water 10 is fed to the tank 20a.
After the water 10 in the work tank T is discharged through the drain 14 as shown in FIG. 12(C) the pump 32 is actuated to supply the oil 11 into the work tank T from the tank 30b. Also the water 10 remaining in the machined recess A1 in the workpiece W2 is suctioned therefrom by actuating the pump 41 at this time.
Then, after the water 10 in the machined recess A is suctioned out, as shown in FIG. 12(D), the oil 11 is supplied to the electrode EL1 by closing the solenoid valve 40, opening the solenoid valve 39 and then actuating the pump 32. Then finish cutting is carried out by using the oil 11 as a working fluid.
In the above background art, the machining fluid supply is arranged such that after performing electrical-discharge machining using water, the water remaining is removed from the machined recess by scattering it using an oil jet or by suctioning it out of the recess. However, such a method for removal of water has the disadvantage of being limited by the design of a jet nozzle provided in the electrode for jetting or suctioning the working fluid. For example, when a groove H formed in the machine recess A2 of a workpiece W3 is small, as shown in FIG. 13(A), it is difficult to provide the jet nozzle in the electrode part so as to oppose to the groove H. Furthermore, while in this case, it may be effective to suction water using the jet nozzle while vertically moving an electrode EL2 within the groove H, complete suctioning of the water is unlikely. Even assuming that the water removal method of the above background art is not restricted to a specific design for the jet nozzle, complete removal of the water is still not possible.
In addition to the above, there is the disadvantage that when machining is carried out by filling the work tank T with oil while water remains in the machined recess, machining will become unstable, and the consumption rate of the electrode will increase, generating unacceptable arc discharges during machining operations.
Of necessity, it can be arranged such that the water is completely removed manually from the machined recess. However, there is then a disadvantage in that automatic change over of the working fluid from water to oil is not possible. Further, in order to manually remove the water, an additional operation of removing the machined workpiece is required which requires additional time and labor. Furthermore, there is such a disadvantage that once the workpiece is removed from the worktable for separating the workpiece in the work tank T, repositioning of the electrode and the workpiece will be required.